JDK 7 added a new transparency slider to the JColorChooser:

The proble
Java 9 adds a new property to AbstractColorChooserPanel to control these sliders:
public void setColorTransparencySelectionEnabled(boolean b);
public boolean isColorTransparencySelectionEnabled();
There is also a new overload of the static JColorChooser.showDialog method to specify that same property:
public static Color showDialog(Component component, String title, Color initialColor,
boolean colorTransparencySelectionEnabled);
Java 9 is expected to be released in March 2017.